1. Field of the Invention
This invention relates generally to athletic shoes, and more particularly to an apparatus and method for providing increased durability, stability and rebound in athletic shoes.
2. Description of Related Art
A recent surge to provide footwear which is both comfortable and anatomically beneficial has resulted in a plethora of ideas having varying degrees of effectiveness. Most of these ideas are merely variations of ideas which have been around for years. Historically, there have been a number of attempts to increase the cushioning and control of an athletic shoe by making modifications to the midsole, which is that material which generally lies above the outsole. The development of the midsole has led to shoes which take into account the physiology of the foot. The numerous attempts to provide superior cushioning in athletic shoes have led to three broad categories of developments, two of which involve the midsole directly.
The first broad category utilizes different materials and configurations of the midsole to improve cushioning as well as provide effective foot control. For example, materials of different hardnesses may be used to provide cushioning and foot control, or a variety of devices may be encapsulated in a midsole to increase cushioning. This type of show has the disadvantage of a short life due to breakdown of the materials used to form the midsole. Since many shoes use only ethyl vinyl acetate EVA or polyurethane (PU) for cushioning, the cells of these foams have a tendency to break down and thus diminish the usefulness of the shoe.
The second category of device utilizes pneumatic devices within the midsole. An example of this is taught in U.S. Pat. No. 545,705, issued to McDonald. The McDonald device is an elastic air filled cushioning device which is incorporated into the heel of a shoe to provide cushioning. A similar device is taught in U.S. Pat. No. 1,498,838 to Harrison Jr. which uses a number of tubes which lie within the midsole. These tubes are inflated by a valve to maintain a pressure above ambient. The tubes in the Harrison Jr. device are made of a flexible inelastic material.
The disadvantages of encapsulating gas within the midsole of a shoe are numerous. It is exceedingly difficult and costly to encapsulate gas in a material. It is much easier, for example, to cut a piece of conventional midsole material such as ethyl vinyl acetate (EVA) to a desired specification than to make a container which retains pressurized air or other gas. The problem of diffusion of gas from a container can be somewhat decreased by using large molecule gases as the encapsulated gas. Using such a gas is expensive and as such increases the expense of manufacturing such a shoe.
Material puncture is also a problem with pressurized gas midsoles. Again, while this problem might be somewhat diminished by careful material selection, the problem of puncture nevertheless exists and the solution to such a problem can add additional manufacturing expense. Yet another serious drawback with this type of shoe is that the pressure of the gas within the encapsulating container is temperature dependent. As such, the stiffness of the shoe varies as the shoe warms up. Similarly, the shoe may respond differently in cold and warm temperatures. Along these same lines, the midsoles are altitude dependent, which means that the shoe will have different support characteristics depending on what altitude it is used at.
Rear foot control and stability is another problem with shoes which encapsulate gas within the midsole. In simple terms, encapsulated gas midsoles are oftentimes too mushy to give proper support.
In light of the multitude of problems associated with gas-encapsulated midsoles, it is of great importance to find alternatives which provide both adequate cushioning, stability and support. Such alternatives must be economical and must eliminate the problems of encapsulated tube technology without sacrificing cushioning.
The third broad category of devices which are intended to increase the cushioning of a shoe include devices which modify an outsole. An outsole is typically made of material such as rubber, polyurethane (PU), thermoplastic rubber (e.g., EVA) and the like. These materials are chosen for outsoles because they are wear resistant. Typically, these materials have fairly good memory characteristics. That is, if the outsole material is deformed either by compression or bending forces, it tends to return to its original shape. The best example of a shoe which falls into this third broad category is U.S. Pat. No. 4,372,058 to Stubblefield, which teaches an outsole in which the periphery of the heel of the outsole maintains the remaining portion of the heel of the outsole in a spaced apart relationship to the ground. This configuration is known as a cantilever outsole. The cantilever configuration helps to redirect vertical forces while increasing energy return to a runner.
In the Stubblefield patent referred to above, an outsole is provided which has a plurality of lugs or levers which extend from the periphery of the bottom of the outsole. These lugs are designed to redirect vertical forces on the outsole so that the forces have at least a horizontal component thereby reducing the stresses on a runner. The Stubblefield patent provides a shoe which provides both cushioning and stability.
One object of the present invention is to improve the design of the Stubblefield shoe by providing even better stability and rebound characteristics and to provide a shoe which utilizes a minimum amount of the heavy outsole material found in conventional outsoles.